Note: Descriptions are shown in the official language in which they were submitted.
~ ~ CASE 4331
3~
- TUBE E~PANDING
BACXGROUND
'~ The present invention relates to tube expansion~
and more par~icularlr to controlled expansion of a ~ube with-
in a ~ube sheet or wi~hin ano~her ~ube using a pressurized
~luid system.
Steam generators used in co~nercial nuclear power
plants a~e heat exchangers including a vessel containing a
large number of stainless steel ~ubes affixed at ~heir ends
to tube sheets. In some steam generators~ namely, the "U"-
tube" type~ the tubes are formed in the shape of a "U" with
both ends afixed to a single tu'be sheet. In other steam
generators, nameIy, the '~once-through" type, the tubes are
straight znd affixed between two separate tube sheets. Typi-
cally, heated radioactive high pressure reactor core primary
coolant is directed through the tubes. A relatively cool, low
prcssure secondar~ coolant, typically water, is pumped through
the steam generator around the hot tubes to thereb~ gain heat
and to vaporize into steam, thus the name "steam generator."
The steam generator tubes are exposed to a hostile atmosphere
of undesirable chemicals, temperatures and temperature gradi-
ents that result in the degradation of the tubes' integrity.
Por example, corrosive chemical action that cccurs during
alternate wetting and drying of the tube surface in a vapor-
liquid mixture atmosphere leads to a failure mechanism known
as stress-corrosion cracking. Another mechanism leading to
tube failure is vibration induced errosion.
However, regardless of how the steam generator tube
fails, the result is a lea~ and a flow of radioactive high
~0 pressure primary coolant into the lo-r pressure secondary
1 ,,
,~,
I ~ ~2033~ ~ CASE 4331
coolant. A cer~ain number of these leaks are tolerable. How-
ever, l.~hen leakage occurs to the extent that the secondary
coolan~ becomes unacceptably radioactive it becomes necessary
to replace or plug the tubes. In that replacing tubes is a
difficult operation, especially in the case of ~he U-tube type
steam generator, the tubes are typically plwggedj Unfortunate-
ly, as ~ore tubes are plugged, the capacity of the stçam genera-
tor is decreased. Eventually, the capacity of ~he s~eam genera-
tor ~ill be decreased to such a degree that large scale over-
haul is required.
The foregoing inevitability can be circumvented to
some extent by stiffening ~he tubes in the vicinities of defects
before the defects become leaks. Hereinafter, a "defective
tube" is deined as a tube having a degraded wall thickness but
not a leaking tube. It may be desirable ~o plug the tube rather
than stiffenlng it once the defect has surpassed 40% of the
wall thickness. Defective tubes can be identified by known
tube inspection techniques. Furthermore, as a precautionary
measure it is deslrable to stiffen tubes in areas of the steam
2(3 generator which experience high 1uid velocities where the like-
lihood of vibration induced erosion is increased.
,J lo stiffen the tubes, typically, a sleeve of suffi-
cient length to cover the defect and to allow expansion of the
sleeve into the tube above and belo~ the defect is inserted
within the tube and positioned at the defect location. The
sleeve and tube are then expanded above and below the deect
to hold them together and thereby stiffen the defective portion
of the steam generator tube.
Several methods and devices are available in the
prior art for expanding the sleeve ~ithin the tube. Rogers,
Jr. et al (U.S. Pat. No. 4,069j573) described a hydraulic tube
expander that applies fluid pressure to the inside o the
sleeve to expand it înto the steam generator tube. Hereinafter,
~ ~ CASE ~331
~2~33~
--3--
the term "hydraulic" expander refers to an expander utiliziIlg
fluicl ~liquid or gas) pressure ~o effect expansion. In Rogers,
Jr. et al, a set expansîon pressure is irst applied within
the fixed tube, then an additional fixed volume of fluid is
~ 5 forced into the system volume. This method and device suCfer
from several dra~backs. I'irst, ~he fluid is applied directly
to the inside of the sleeve. This requires a ~ood seal between
Y the expander device and the sleeve, thus, an accurate sizing
of the slee~e's insid0 diameter is cri~ical. Also~ the sleeve's
19 inside surface must be extremely smooth. These requirements
add signiicantly to the sleeve cost. Second, this device
spills undesirable fluid into the steam generator necessitating
clean-up and repriming of the apparatus before the next expan-
sion. Third, the method of applying a fixed fluid pressure
follo~red by a fixed volume irlput results in a steam generator
tube outside diameter increase which is controllable to with
in about .02S inches. This degree of expansion control is
not acceptable if the tubes are ever to be withdral~n from the
tube sheets for replacement i.e., when enough -tubes are damaged
to so warrant rebuilding of the steam generator. An expansion
o .025 inches l~ill preclude ~rithdrawal of the tube without an
unacceptable risk of damage to the tube sheet. This is a
particular problem in the once through steam generator where-
I in the only way to remove the tube is through a tube sheet.
An acceptable degree of steam genera~or tube outer diameter
expansion control is about .006 inches or less, which will
allow withdralral o the steam generator tubes through the
tube sheet~
~ The reason the method of the prior art cannot achieve
¦ 30 the desired expansion control is that, because of variance in
the dimension and yield strengths of the sleeves and the tubes,
one cannot calculate what fluid pressure to apply to the system
or volume of fluid to inject into the system~ unless the dimen-
sions and yield strengths of the particular sleeve and tube
I
~ LZ03368 ~ CAS~ 43~1
! undergoing expansion are known. Unfortunately, these values
fl vary due to manufacturing tolerances and in-service material
¦ property transitions. Each case is differen~. Treating each
¦ expans~on uniformly as in the prior art limits control of the
~ 5 steam generator tube outer diamete~ to about within .G25 inches.
There ore, one cannot calculate the fluid pressure, or volume
of fl~id in~roduced to ~he sys~em or decrease in system volume,
or predetermine a distance to expand based on test specimens
and then proceed willy-nilly expanding hundreds o tubes in
lr~ a nuclear steam generator. Unless, of course a one can accept
the degree of control that results.
Similarly, the compressable elas-tormer device of
Rogers, Jr. et al., is, in fact, incapable of controlled
expansion of the tube to within .006 inches.
The present invention overcomes these disadvantages
of the prior art. Fluid pressure is used to expand a disten-
sible polyurethane bladder within the sleeve to expand the
sleeve into the ~ube. The fluid is contained at all times
w:Lthin the bladder, thus there is no spillage and no need for
2.0 reprlming of the expander sys1em.
The degree of expansion o the steam generator tube
outcr diameter is controlled within .006 inches by determining
in each case exactly when the steam gen~rator tube begins to
yield. This is accomplished by monitoring the change in
pressure (dP) of the fluid as a function of the change of the
volume ~dV) o~ the fluid system exclusive of the distensible
bladder. It is most ;mportant to note here that d~r represents
the volume of the 1uid system exclusive of the distensible
bladder. According to one embodiment of the invention~ the
change in pressure, dP, of the system fluid is compared to
the change in volume dV. The fluid pressure, P, of $he
system, will increase linearly relative to dV until the yield
point pressure of the sleeve material is reached. As the
sleeve yields, the pressure increases at a slower rate rela-
.
~ 3~ CASE 4331
-5-
i
tive to dV since the bladder is distending, thus adding volume
to the total system and lessening the net decrease in the
~ total volume of the system inclusive of ~he bladder volume.
! ~en the sleeve con~acts the inside surface o the steam
~ 5 genera~or tube, the pressure will increase at a higher rate
with respect ~o dV until ~he yield streng~h of the steam
generator tube is reached. Again9 when the pressure begins
to increase at a slower rate with respect to dV ~he steam
generator tube has begun to yield and expand. This is the
critical point. The variance of dimensions and material
properties of the steam generator tube and the sleeve pre-
cludes precise calculation of this point using the prior art
methods. By monitoring the pressure rate of change with
respect to dV according to the present invention, this point
where the steam generator tube begins to yield can be deter-
mined ~iith precision in each and every case. In this wayJ
the cxpansion of the steam generator tube outer diameter can
be controlled to within the .006 inch tolerance.
In another embodiment, rather than incremen-tally
decreasing the volume of the f:Luid system, a mass pump adds
an incremental fluid mass, d~, to a fluid system having a
fixed fluid volume (fixed volwlle exclusive of the expansion
ar~GI~ as discussed above). Hereinafter a "volume pump" is
I defined as a positive displacement pump wh:i.ch acts to increase
Z5 or decrease pressure of a fluid system by controllably effect-
ing the volume of the fluid system. Hereinaf-ter a "mass pump"
is defined as a positive displacement pump which acts to
increase or decrease the pressure of a fluid system by con-
trollably efecting the mass o-f the fluid system. Whether a
volwne pump or a mass pump is used, the fluid system pressure
is monitored as a function of the pump incremental action to
determine the onset of plastic deformation of the sleeve and
tube.
It is an object of the present invention to provide
I ( lZ03368 CASE ~1331
a me~hod of con~rollably expanding tubes within a .006 inch
limit.
It is a urther object of the present invention to
provide a method having the foregoing advantage and which
- 5 determines the yield point of the tube on a case-by-case basis.
It is a further object of the present invention to
provide a hydraulic tube expander utilizing an expandable
bladdel to there~y contain ~he hydraulic fluid to prevent
fluid spillage and eliminate the need to clean the steam
~enera~or or ~o reprime the apparatus between expansions.
Other objects and advantages of the present inven-
tion will be readily apparent from the following description
and drah-ings which illustrate pre~erred embodiments o the
present invention.
IS SU~IARY OP THE INVENTION
. . . _ .
The present invention involves a method and appara-
tus ~or hydraulic tube expansion. In the method, a sleeve is
expanded within a tu~e and secured there to by incrementally
decreasing the volume of the expander system 1uid exclusive
o the ~xpander ~hich will inherently experience an increase
in ~luid volume as it expands. The rate of system pressure
increase in monitored as a function of incremental volwne
change. Two critical rate decreases occur during use of the
apparatus. The first decrease indicates the onset of plastic
expansion of the sleeve. The second decrease indicates the
onset of plastic expansion of the tube. The tube outer dia-
meter can be expanded accurately to within six thousandths
o an inch (.006 inch). Alternative to decreasing the system
volume the 1uid system mass can be incrementally increased
with the same results. In the apparatus, system 1uid is
contained within a sealed distensible bladder expander.
BRIEF DESCRIPTION O~ THE DRAI~INGS
. .. . . _
~ CASE 4331
3~6
-7-
FIG. 1 is a graph illustrating the method of the
- present invention.
FIG. 2 is a schema~ic view of a hydraulic tube
expanding sys~em according to the presen~ invention.
FIG~ 3 is a cross section view of the hydraulic
tube expander accordin~ to one embodiment of ~he inventi~n.
DETAILED D~SCRIPTION OF T7~E PREFERRED EMBODI~IENTS
Refer now to FIG. 1 ~here being shown a graph
illustra~ing the method according to the present invention.
Plotted in FIG. 1 is the system 1uid pressure as a function
of incremental pump action. Pump 40 ~FIG. 2~ is a volume
pump ~hlch incrementally decreases the volume of a fluid
chamber ~not shown) therein. Alternatively pump 40 may be a
mass pump which incrementally increases the fluid system mass.
~IG. 2 repre~ents both embodiments with pump 40 be~ng either
a volume pump or a mass pump. The end result is the same as
it will become clear from the -~ollowing description.
First consider the utilization of a volume pump.
In operation, the incremen~al decrease in pump volume causes
~0 t~io re~lated effects: (1) an increase in system pressure, and
~2) an expansion of the repair sleeve and steam generator
tube. Obviowsly~ the less the sleeve and tube expand to
thereby add volume to the total fluid system, the greater the
increase in pressurs per incremental volume decrease of the
system exclusive of the expander. The fluid system pressure
is indicative of the relative resistance to sleeve and tube
expansion. As the sleeve and tube expand elastically the
resistance to expansion is relatively high. As pressure is
increased and the slee~e and tube yield points are reached the
sleeve and tube begin to expand plastically and the resistance
!
j~
.. ~,
~ ~ CASE 4331
~ ~33~
--8
to expansion is rela~ively lo-~.
Curve 52 of FIG. 1 illustrates the expansion of a
- repair sleeve within a ~ube. As the pump incrementally de-
creases ~he ~luid volwne of ~he system, the fluid is compressed,
the sys em fluid pressure increases~ and the sleeve is expanded
elastically. At point 53 ~he sleeve makerial reaches the
yield ?olnt. Between point 53 and point 55 the sleeve expands
plastically. The slope of curve 52 between points 53 and 55
has decreased because the sleeve's resistance to expansion has
decreased. As the sleeve expands, volume is thereby added *o
the total 1uid system in the vicinity of the expander ~although
net system volume is being decreased by the pump action.) ~ore
volume is added due to sleeve expansion during plastic defor-
mation per incremental volume decrease in the pump (or in the
system exclusive of the expander), dV, than is added during
elastic deforma~ion o~ the sleeve. The net effect is a rela-
tively lower total system volurne decrease per incremental
-
volume decrease in the pump during plastic deformation then
during elastic deformation of the sleeve. The system fluid
pressure is inversely proportional to the system fluid volume
~assuming, of course, that a constant fluid mass is maintained).
~; At point 55 the sleeve contacts the tube. Curve 52
between points 55 and 57 represent the elastic expansion o~
the tube. At point 57 the tube begins to yield and expand
plastically. Points 53 and 57 will not always occur at the
same pressure.- Each tube and sleeve are different in material
dimensions and properties. By determining point 57 from each
and every expansion the increase in the tube outside diameter
can be maintained within .006 inches for typical steam genera-
tor si~e tubes. Curve 52 above point 57 represents the plas-
: tic expansion of the tube and â leeve.
Turn now to FIG. 2, there being sho~Yn a tube expan-
der system according to the present in~ention. In FIG. 2
sleeve 22 is to be expanded into steam generator tube 24~
, ;
,,~ . . _ ~.
CA.SE 4331
rhe expanding apparatus, explained below in more detail,
inclu~es a dis~ensible polyurethane bladder 10. Bladder 10
- and sleeve 22 are appropria~ely positioned for the expansion.
This is easily accomplished by first expanding bladder 10 to
hold sleeve 22 and then inserting them both into tube 24.
Fluid suppl~ conduit 31 establishes fluid communication from
reser~joir 44 to expander supply tube Z0. Con~rol volume ~or
control mass) pump 40 is in fluid communication with conduit
31 via conduit 33. Pump 40 incrementally decreases the
volume of a chamber therein (no* shown). The chamber is in
fluid comrnunica~ion wilh conduit 33. Valve 48 is positioned
on conduit 31 bet~een reservoir 44 and conuit 33. Valve 50
is positioned in conduit 31 between conduit 33 and expander
supply tube 20. Pressure sensor 34 senses the fluid pressure
within conduit 31 and generates a signal through cable 45 to
computer 36. Computer 36 is programmed to generate a signal
through cable 47 to display~.3g which displays the pressure
as a graph according to FIG. 1. Controls 32 enable an opera-
tor ~not shown) to instruct and control computer 36 by communi-
cating therewith via cable 49~ Computer 36 generates a signal
to pump ~0 through cable 51 to incrementally decrease the
fluid volume of the system (or incrementally increase the mass).
Computer 36 is programmed to monitor the incoming pressure
signal as a function o~ incremental pump action (~olume
decreases or mass increase) and to indicate via display 39 a
change in slope of the curve thereby enabling precise detection
of the onset of plastic deformation of sleeve 22 and tube 24.
To explain operation in further detail a typical
set of dimensions will be given as follows.
Steam generator tube outside diame~er .627 inches
Steam generator inside diameter .551 inches
S.leeve outside diameter .525 inches
Sleeve inside diameter .430 inches
~ ~203368 ~` CASE 4331
-:10 -
~lso, Pump 40 decreases ~he volume of its chamber with an
accuracy iner than .001 cubic inches. Total system volume
- is approximately 0.5 cubic inches.
To begin the procedure, valve 50 is closed and
s valve 13 is open. Pump 40 is turned on and dra~Ts 1uid in~o
its ch .ber. Valve 48 is now closed and valve 50 opened.
Pump 43 now acts to increase the system pressure to expand
bladdeL 10 enough to grip sleeve 22. Air can be removed from
*he fluid system by bleeding a~ plug 15 ~FIG. 3~ if desired
but if not, the operation of ~he system will not be affected.
The 1uid of the preferred embodimen~ is glycerin.
Sleeve 22 is positioned in tube 24 at the location
to be stiffened. Pump 40, under the direction of computer 36
begins to decrease its chamber volume. At a volume decrease
of~ for example, .175 cubic inches and system pressure of
for example, 117000 pounds per square inch (PSI) sleeve 22
yields and begins plastic deformation. This is represented
by point 53 of PI~. 1. Computer 36 senses the change i~ slope
of the curve 52 as explained above in regards to FIG. 1 and
2~ stops pu~lp ~0.
The operator ~not shown) views display 39 and in-
structs computer 36 via contro:L 32 to proceed. Pump 40 is
reactivated. At a total volume decrease of, for example,
.200 cubic inches and a pressure of, for example, 14,000 PSI,
computer 36 senses another sloFe change as sleeve 22 contacts
tube 24. This occurrance is represented by point 55 of FIG.
1. At this point sleeve has been expanded .010 to .030 inch.
At a volume decrease of, for example, .236 cubic inches and a
pressure of, or example, 21,000 PSI~ computer 36 senses
another slope change as tube 24 begins to yield~ This is
represented by point 57 of FIG~ 1. Pump 43 is deactivated.
At this point tube 24 has increased its outer diameter by
about .002 inches.
1203368 CASE 4331
-11-
Two phenomena of ma~erials are ~orth noting here.
First, ~hen the tube is expanded "plastically" it is not truly
plastic deformation. The material maintains elastic character-
îstics zo a certain degree. The second phenomenon is that as
~ 5 the ~ube is expanded it is "work-hardened" and becomes more
elastic and less plastic. The pertinent effect of ~hese pheno-
mena is that when the expanding force is relieved the material
will spring back someT~Ihat. This effect is on the order of
~001 inches of outside diameter in the presen~ example.
- Once yield point 57 has been determined, the re-
mainder of the expansion is accurately predic~ed. In the
present example a further decrease in pump volume to .244 cubic
inches decrease total yields tube 24 to .006 inches outside
diameter increase~ or .633 inches total outside diameter.
Relieving the expanding pressure, tube 24 springs back to
.632 inches, a resulting .005 :inch increase. The expansion
is sufficient to adhere sleeve 22 to tube 24 but not enough
to preclude subsequent removal of steam generator tube 2
through the tube sheet ~not sho~m).
Of course, the ends of sleeve 22 are expanded both
below and above the area of degradation of tube 24, to effec-
tively stiffen the tube.
As noted, the above described embodiment pertains
to a volume control pump 40 that incrementally decreases the
volume V of the system exclusive of the bladder. Alternatively,
fluid mass could be incrementally added to the system with
control mass pump ~0 while maîntaining a constant volume, V,
with the same results. System pressure is maintained as a
function of incremental pump action. In the case of a control
mass pump, this incremental action represents the increase in
system mass while a constant system volume exclusi~e of the
expander, ls maintained. The method as hereinbefore discussecl
is the same~ regardless of the use of a control mass pump or a
control volume pump.
I ~ ~ CASE 4331
~3- ~2~
Turn no~r to FIG. 3 wherein a cross-section view of
a ~ube expander according ~o the presen~ invention is shown.
Distensible bladder 10 is a hollow polyure~hane cylinder having
~ a bladder tubing end 37 and a bladder plug end 38. The inside
diame er o~ bladder 10 defines chamber 11. Bladder 10 has a
first outside diameter 60 for its midsection, and a decreasing
di~me,er 61 to a smaller second outside diameter 62 at ends
37 and 38~ Ends 37 and 38 having decreasing diameter 61 and
second diame~er 62 serve to be self sealing to prevent leakage
of fluid, As fluid pressure increases, ends 37 and 3g are
forced against mating surfaces of tubing endfitting 16 and
plug endfit~ing 14 thereby sealing bladder 10. Decreasing
diameter 61 is provided to prevent shearing of the midsection
o bladder 10 from ends 37 and 38. Bladder 10 is reasonably
elastic and has a high tensile strength~ Polyurethane having
a hardness between 60 on the Shore A scale and 75 on the Shore
D scale is acceptable. In the preferred embodiment a polyure
thane of 92 Shore A is used. Also the tensile strength of
bladdcr 10 should be greater than about 5,000 PSI. In the
preferre~d embodiment bladder 10 has a tensile strength of 6,200
PSI.
Stud 12 extends through chamber 11 and protrudes
~'! frorll both ends 37 and 38. The protruding stud tubing end 41
and stud plug end 42 o:E stud 12 are threaded. First bore 18
2~ extellds longitudinally through stud 12. Second bore 19 extends
fr~m the surface of stud 12 to bore 18 to establish fluid
communication between bore 18 and chamber 11. Tubing endfitt-
ing 16 has a longitudinally extending tubing endfitting stud
bore 26 threaded to accept stud tubing end 41, and a longi-
tudinally extending tube bore 28 threaded to accept the end
of threaded supply tube 20. Tube 2n extends through tube bore
28 and protrudes into tubing endfitting stud bore 26. Tube 20
may be soldered to tubing endfitting 16 with solder ~3 if
desired, but this is not necessary if supply tube 20 and tubing
.,
~33 Ei~ ~
CASE 4331
-13-
endfitting 16 are properly threaded. Pl;able nylon tube 17
serves ~o protect tube 20 extending therethrough.
Plug endfitting 14 has longitudinally extending
plug endfitting stud bore 30 threaded to accept stud plug
- 5 end i2~ longitudinally extending plug bore Z9 threaded to
accept plug 15~ and bleed bore 27 establ;shing fluid communl-
caticn beLIreen plug endfi~-ting s~ud bore 30 and plug bore 29.
Plug 15 has hex socket 25 and tapered point 21.
Point 21 seats in bore 27u Plug 15 can be removed for bleed-
ing -the fluid system if desired. Bores 2O and 30 o~ the end-
fittings 16 and 14 respectiYely have an inside diameter ormed
to mate with ends 37 and 38 of bladder 10. Actually, an in~er-
~erence *it is desirable to effect a better seal.
Upon assem~ling the apparatus as sho~rn in ~I~. 3
bladder 10 is sealed by endittings 1-~ and 16 and st~d 12.
The 1uid path extends rom supply tube 20 to chamber 11 o
bladder 10 via bores 26, 18 and 19.
It should be noted th~t 21-ternatively more -than one
bladder could be utiLi~ed with an extending ~itting positioned
therebet~een. Ho~rever, there l~ould be a resultin~ decrease in
the controllzbility o the expansion due ito the sleeve and
tubc property variance bet~reen the t~ro points bei~g expanded.
Although computer 36 is utilized, adding -to the
precision o the system, thc inven~ion is not limited thereto.
~anual cont~ol o the system l~ill yield equ211y e~ec~ive
~esults.
The above description and dra~vings are only illus-
trative of one embodimen~ IYhich achieves the ob~ects~ features
and advantages of the present invention, a~d it is not intended
th~t the present invention be limited thereto~ -
Any modification Or the present invention ~hich comes
~ithin the spirit and scope of the ollo~ing claims ls considered
part of the present invention.
~, ~ "
